Mobility in connection with wireless communication networks is usually a precondition. The ability to move within a wireless network and/or between various wireless networks is particularly desirable in connection with wireless mobile terminals, e.g. such as cell phones or similar communication devices, or such as laptops or similar computer devices provided with wireless communication ability, e.g. equipment for communication with Wireless Local Area Networks (WLAN, e.g. WiFi), or equipment for communication Worldwide Interoperability for Microwave Access networks (WiMAX networks, based on IEEE 802.16), or equipment for communication with General Packet Radio Service system (GPRS system based on 3GPP specifications), or Universal Mobile Telecommunication System (UMTS, based on 3GPP specifications) or enhancements of the UMTS such as the Long Term Evolution (LTE) or similar.
Traditionally, upon attachment of a wireless mobile terminal to an access point, e.g. such as a base station or similar of an IP based wireless communication system, the system selects a gateway as the IP point of presence for that terminal. Once the terminal is attached it can be reached via the IP address or similar of this gateway. For example, in GPRS this gateway is the Gateway GPRS Support Node (GGSN) and in LTE this gateway is the Public Data Network Gateway (PDN Gateway or simply P-GW).
The gateway now mentioned can be seen as a mobility anchor for the mobile terminal, since it is maintained as the point of presence even if the terminal moves away to other access points, i.e. the terminal can always be reached via the IP address or similar of the IP anchor even if the terminal moves and changes its point of attachment to the wireless communication system. Indeed, the terminal remains anchored to the initial gateway, even if the movement means a relatively long distance. This kind of mobility anchors is well known in the art and they need no further description. Various mobility anchors are e.g. frequently used in connection with IPv4 and IPv6.
If the anchor gateway is far away from the mobile terminal, it may require considerable transport usage to get traffic to/from the terminal, especially in the frequent case when the mobile terminal communicates with geographically close peers or similar partners. This waste of transport resources is called the tromboning effect.
The tromboning effect is clarified with respect to FIG. 1 illustrating an exemplifying wireless communication system 100. The exemplifying system 100 comprises a plurality of Mobile Terminals 115a, 115b and a Packet System 110. The Packet System 110 comprises at least one Mobility Node Arrangement 111, a plurality of Serving Nodes 112a, 112b, a plurality of Access Points 113a, 113b, 113c, 113d and a plurality of Mobility Anchors 114a, 114b. The Mobility Anchors 114a, 114b may e.g. be Gateway Nodes or similar. The lines and arrows or similar connecting the different devices, nodes or similar arrangements of the Packet system 110 in FIG. 1 intend to illustrate connectivity between these arrangements. For example, the Packet System 110 is configured to communicate with the Mobile Terminals 115a, 115b via a radio interface. The arrangements 111, 112a, 112b, 113a, 113b, 113c, 113d, 114a, 114b within the Packet System 110 are preferably configured to communicate with each other by means of data packets, e.g. such as IP packets or similar.
Wireless communication systems as the system 100 in FIG. 1 are well known to those skilled in the art and they need no detailed explanation. Nevertheless, a brief overview of the arrangements in the system 100 will be given below.
The Access Points 113a-113d of the Packet System 110 is usually transceivers configured to communicate data packets via a wireless radio interface between the Mobile Terminals 115a, 115b and the Packet System 110.
The Mobile Terminals 115a, 115b may be any device used directly by a user to communicate with an Access Point 113a-133d. It can be a hand-held telephone, a card in a laptop computer or any other device that is configured to connect to an Access Point 113a-113d. It is assumed that the Mobile Terminals 115a, 115b moves substantially freely around the Access Points 113a-113d. It is also assumed that the Mobile Terminals 115a, 115b communicate via the Packet System 110 and the Access Points 113a-113d, i.e. the Mobile Terminals 115a, 115b do not communicate directly with each other.
The Mobility Node 111 manages the mobility functions in the communication system 100. For example, assume that a Mobile Terminal 115a moves from a first access point 113a to a second access point 113b as illustrated by dashed lines in FIG. 1. The Mobility Node 111 will then manage a transfer or a handover or similar from access point 113a to access point 113c such that the services and/or context etc associated with the Mobile Terminal 115a is now provided via access point 113c. In particular, the Mobility Node 111 is configured to manage user-data bearers Ld, Ls (to be explained further later) for communicating user-data of a Mobile Terminal 115a, 115b between a Serving Node 112a, 112b and a Mobility Anchor 114a, 114.
The Serving Nodes 112a, 112b are configured to communicate user-data for a Mobile Terminal 115a, 115b between a Mobility Anchor 114a, 114b and an Access Point 113a-113d. The Serving Nodes 112a, 112b gets orders from the Mobility Node 111 to establish, modify and release bearers between the Serving Nodes 112a, 112b on one hand and the Access Points 113a-113d respectively on the other hand, but also between the Serving Nodes 112a, 112b on one hand and the Mobility Anchor 114a, 114b respectively on the other hand.
The Mobility Anchor 114a, 114b are the interfaces between the internal IP network of the Packet System 110 and various external IP networks such as the Internet or similar Public Data Networks (PDNs) 116.
FIG. 1 intends to illustrate the movement of a mobile terminal over a long distance in that the Mobile Terminal 115a has moved from the first access point 113a to the second Access Point 113b as illustrated by dashed lines.
Now, assume that the Mobile Terminal 115a was anchored at the first Mobility Anchor 114a. It will then remain anchored at the first Mobility Anchor 114a, even if the new position at the second Access Point 113c would make it more beneficial to anchor the terminal at a second Mobility Anchor 114b being locally arranged with respect to the second access point and/or the Serving Node 112b serving the second Access Point 112b so as to enable a local flow of user-data. For example, this may be the case if the first Mobile Terminal 115a communicates with a second Mobile Terminal 115b anchored at the assumedly local second Mobility Anchor 114b as shown in FIG. 1. However, since the distant first Mobility Anchor 114a is still the anchor for the first Mobile Terminal 115a the flow of user-data between the Mobile Terminals 115a and 115b will pass through the distant first Mobility Anchor 114a and not through the local second Mobility Anchor 114b as would be preferred.
The preferred local flow of user-data between the second Mobility Anchor 114b and the second Serving Node 112b has been indicated by a solid line Ls in FIG. 1 (c.f. B-new in FIG. 2). The distant flow of user-data between the first Mobility Anchor 114a and the second Serving Node 112b has been indicated by dashed line Ld in FIG. 1 (c.f. B-old in FIG. 2).
The flow of user-data through a distant path instead of an alternative local path causes a so-called tromboning effect as previously mentioned.
One way of mitigating the tromboning effect may be to detach the Mobile Terminal 115a from the Access Point 113c and the Packet System 110 and then re-attaching it to the same Access Point 113c again while selecting a new anchor in the form of the second Mobility Anchor 114b that is more suitably located in the Packet System 110. However, this means that session continuity for the Mobile Terminal 115a and/or maintenance of the context etc for the Mobile Terminal 115a can not be guaranteed. This is typically not acceptable since session continuity is a fundamental principle in many modern wireless communication systems, e.g. such as the LTE systems and other systems according to the 3GPP specifications. In other words, this solution cannot be applied in case session continuity is to be guaranteed for a given terminal.
Hence, there is a need for an improved solution that relocates a mobility anchor while mitigating or avoiding one or several of the disadvantages touched upon above.